Transmission line elements are sometimes used to create balanced transformers, unbalanced transformers, and balanced-unbalanced transformers (also referred to as baluns). These transformers may be used in integrated circuits such as radio-frequency (RF) power amplifiers and low noise amplifiers that operate at high frequencies.
Several ongoing challenges that confront RF power amplifiers are finding ways to improve power efficiency and linearity. Push-pull power amplifiers may have up to four times higher load impedance for a given power level than do conventional single-ended power amplifiers. This may allow for much lower loss in frequency bands below 500 megahertz (MHz). For higher frequency applications (e.g., 800 MHz and beyond) for compact and portable devices, the baluns, particularly those baluns used for output matching, may be prohibitively large or inefficient.